Approaching the quantum limit with optically instrumented multimode gravitational-wave bar detectors

Richard, J. P.

doi:10.1103/physrevd.46.2309

Cited by 28 publications

(9 citation statements)

References 18 publications

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“…Reflexion of light by a high-finesse Fabry-Perot cavity is very sensitive to changes in the cavity length. Such a device can thus be used to monitor displacements of one mirror of the cavity, as it has been proposed for gravitational wave bar detectors where the mirror is mechanically coupled to the bar [15,16], or for the detection of Brownian motion in gravitational wave interferometers [17,18]. In this letter we report a high-sensitivity observation of the Brownian motion of internal modes of a mirror.…”

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confidence: 98%

High-sensitivity optical measurement of mechanical Brownian motion

et al. 1999

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We describe an experiment in which a laser beam is sent into a high-finesse optical cavity with a mirror coated on a mechanical resonator. We show that the reflected light is very sensitive to small mirror displacements. We have observed the Brownian motion of the resonator with a very high sensitivity corresponding to a minimum observable displacement of 2 × 10 −19 m/ √ Hz.PACS : 05.40.Jc, 04.80.Nn, 42.50.LcThermal noise plays an important role in many precision measurements [1]. For example, the sensitivity in interferometric gravitational-wave detectors [2-4] is limited by the Brownian motion of the suspended mirrors which can be decomposed into suspension and internal thermal noises. The latter is due to thermally induced deformations of the mirror surface. Experimental observation of this noise is of particular interest since its theoretical evaluation strongly depends on the mirror shape and on the spatial matching between light and internal acoustic modes [5][6][7][8][9]. It is also related to the mechanical dissipation mechanisms which are not well known in solids [10]. Mirror displacements induced by thermal noise are however very small and a highly sensitive displacement sensor is needed to perform such an observation.Monitoring extremely small displacements has thus become an important issue in precision measurements [11] and several sensors have been developed. A technique commonly used for the detection of gravitational waves by Weber bars is based on capacitive sensors [12]. Another promising technique consists in optical transducers [13,14]. Reflexion of light by a high-finesse Fabry-Perot cavity is very sensitive to changes in the cavity length. Such a device can thus be used to monitor displacements of one mirror of the cavity, as it has been proposed for gravitational wave bar detectors where the mirror is mechanically coupled to the bar [15,16], or for the detection of Brownian motion in gravitational wave interferometers [17,18]. In this letter we report a high-sensitivity observation of the Brownian motion of internal modes of a mirror. The sensitivity reached in our experiment is better than that of present sensors and comparable to

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confidence: 98%

High-sensitivity optical measurement of mechanical Brownian motion

et al. 1999

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“…We have been attracted by the possibilities offered by optical readout systems, as vigorously developed for interferometric GW detectors, and more recently applied in connection with cryogenic bar GW detectors [6,7]. We take a Fabry-Perot optical cavity as the motion sensor.…”

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Wideband Dual Sphere Detector of Gravitational Waves

et al. 2001

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We present the concept of a sensitive and broadband resonant mass gravitational wave detector. A massive sphere is suspended inside a second hollow one. Short, high-finesse Fabry-Perot optical cavities read out the differential displacements of the two spheres as their quadrupole modes are excited. At cryogenic temperatures, one approaches the standard quantum limit for broadband operation with reasonable choices for the cavity finesses and the intracavity light power. A molybdenum detector, of overall size of 2 m, would reach spectral strain sensitivities of 2 3 10 223 Hz 21͞2 between 1000 and 3000 Hz. This stems, however, from the noise performance of the employed readout systems. A general analysis of the problem, valid for any linear detector, has been given in Ref. [2]. Secondary resonant masses are linked to the main resonant mass to efficiently couple the signal amplitude to the final readout, but then the bandwidth is limited to a fraction of the main resonator frequency. Such a coupling is poorer the smaller the total number n of resonators, and, correspondingly, the bandwidth decreases with n. To open the bandwidth, one would have to use multimode systems [3,4] with n $ 3, but, until now, only two-(mechanical) mode systems have worked their way into operating detectors, giving a fractional bandwidth Df͞f ø 0.1.However, if a single mechanical resonator were driven only by its thermal noise and by a signal force, the signal to noise ratio would be independent of frequency, and thus the band would open up provided enough signal amplitude can be coupled to the final readout. The possibilities offered nowadays by optomechanical systems are such that the interplay between the back-action of the radiation pressure and the photon counting noise in a high finesse, high power Fabry-Perot cavity would allow enough signal coupling [5] to get broadband operation at the Standard Quantum Limit (SQL) (see below).We have been attracted by the possibilities offered by optical readout systems, as vigorously developed for interferometric GW detectors, and more recently applied in connection with cryogenic bar GW detectors [6,7]. We take a Fabry-Perot optical cavity as the motion sensor. In a system under development [7], the length of the sensor cavity is compared to that of a second cavity, separately kept, which acts as a reference. We do not take into account here the noise introduced by the reference cavity, assuming for simplicity that it is negligible. With a sensor cavity length of the order of centimeters, there is no loss of signal strength for finesses F as high as the highest attainable with current technology, F 10 6 , for GW in the kHz range. So we have considerable freedom to vary the finesse and the light power P incident on the cavity, in search for optimal conditions at a chosen frequency, which do not demand unreasonable values for these parameters.Let us then turn to the primary mechanical resonator, whose motion is directly related to the incoming GW. We take into consideration both solid and hollow sp...

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“…A principal role of the optical readout for the classical Weber bar was theoretically investigated in the paper [9]. Afterwards, this idea was developed in [10] and then a pilot model was designed and tested at room temperature [11][12][13]. The possibility of achieving the sensitivity 10 −20 Hz −1/2 for a room temperature bar with a good optical readout has been shown in [14].…”

Section: Equivalent Scheme and Notationsmentioning

confidence: 99%

Reception frequency bandwidth of a gravitational resonant detector with optical readout

Gusev

Rudenko

Cheprasov

et al. 2008

Class. Quantum Grav.

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A gravitational resonant bar detector with a large scale Fabry-Perot cavity as an optical read out and a mechanical displacement transformer is considered. We calculate, in a fully analytical way, the final receiver bandwidth in which the potential sensitivity, limited only by the bar thermal noise, is maintained despite the additional thermal noise of the transformer and the additive noise of the optical readout. We discuss also an application to the OGRAN project, where the bar is instrumented with a 2m long FP cavity.

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Approaching the quantum limit with optically instrumented multimode gravitational-wave bar detectors

Cited by 28 publications

References 18 publications

High-sensitivity optical measurement of mechanical Brownian motion

High-sensitivity optical measurement of mechanical Brownian motion

Wideband Dual Sphere Detector of Gravitational Waves

Reception frequency bandwidth of a gravitational resonant detector with optical readout

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